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Women Scientist Profiles

Marianne Bronner, Ph.D.

Marianne Bronner, Ph.D.

Dr. Marianne Bronner, a developmental biologist at Caltech, studies a cell type called the neural crest, found only in vertebrate embryos. When the nervous system is forming, a flat sheet called the neural plate lies at the midline of the embryo. As the neural plate rolls up into the neural tube, the neural crest cells form the leading edge—then crawl out of the central nervous system into the periphery, where they form many derivatives, including most of the peripheral nervous system, the melanocytes of the skin, and the craniofacial skeleton.  

Understanding the normal development of these cells has important implications for elucidating the origin of birth defects and diseases that affect the neural crest, including cleft palate, familial dysautonomia, Hirschprung’s disease, and cancers like melanoma and neuoblastoma that derive from the neural crest.

Dr. Bronner earned her Ph.D. in biophysics from Johns Hopkins University in 1979. From 1985 to 1996, she was a professor at U.C. Irvine. She has been a professor at Caltech since 1996.

How has mentorship shaped your career?

I had very little mentorship. That’s why I think it's incredibly important. Navigating through a career is sort of like a random walk. You bump into things and make lots of mistakes. If someone can mentor you, you can navigate more quickly and more efficiently.

I spend a good portion of my time mentoring other people. Once you get as old as I am, there are a lot of people you can mentor. Earlier in my career, I had a largely graduate student lab. Now I have mostly postdocs. I also mentor young assistant professors.

It’s important for young people to seek out mentors. If you see somebody that you think you could relate to well, start up a conversation with them. You can keep in touch with them by email and just ask for advice whenever you need it. I wouldn’t ask for a formal mentoring relationship; I would just pursue it.

Name some of the highlights of your career.

I've had a wonderful career. I've been very fortunate. It’s hard to pick highlights. The great thing about this kind of career is, first of all, you can have a big influence on a lot of other people and really help them.

I love the flexibility that one has as a scientist. I thought it was much easier to raise kids, because I had the ability to stay home when they were sick and take them to whatever event they needed to go to. I also love the fact that we get to travel all over the world and see all sorts of wonderful things.

I find the whole idea of discovery so exciting. In a larger group like mine, there’s some cool discovery almost every day.

One of my most cited papers was one that was published about 25 years ago, where we did single cell lineage analysis of cells in the forming neural crest region in chicken embryos. We found that one cell could give rise to multiple derivatives. It was before the whole concept of stem cells, but it showed that these cells had broad developmental potential.

What’s really cool is that recently, in the journal Cell Stem Cell, a paper was published in which the authors examined the same question in a completely different experimental manner. They used confetti mice, where you can use multiple colors to identify precursor cells, and they found exactly the same result. They used an incredibly elegant technology in a different species and came up with the same conclusions that we raised 25 years ago. That’s pretty cool.

What do you think are some of the most exciting recent scientific advances in your field?

Neural crest cells give rise to lots of different derivatives in the embryo. But embryos are really small. One of the enigmas to me was, as the embryo grows, and into adulthood, how do we keep growing? How do you keep adding cells to organs?

There were a couple of papers published last year in Science about something called Schwann cell precursors. The neural crest cells I work on give rise to Schwann cells, which are cells that wrap around nerves and help conduction velocity. When your motor neurons want to make your arm move and it doesn’t take minutes to happen, that is because of these Schwann cells.

These two papers in Science discovered that these Schwann cell precursors are basically stem cells. Even postnatally, they can give rise to lots of different types of cell types, including neurons and peripheral ganglia but also melanocytes, and probably many other things that have yet to be discovered. I thought that was really cool because it helped explain how stem cells are retained into adulthood.

What are the barriers to women in science?

I actually don't think there are very many right now. Right now in science the barriers are uniform for everybody. Everybody's worried about funding. I think in some ways women are our own worst enemies because we get psyched out. I think women get more frustrated and take the challenges to heart.

Today things are very different from when I started out in science. There was one faculty member in my department, in graduate school, who would call up women who were accepted and discourage them from coming, because he didn’t think women could be scientists. This was 35 years ago. It’s just not like that anymore. In fact, we have as many female graduate students in most classes as men, and sometimes more. The real problem now is the leaky pipeline—that women often drop out of science at every step along the way, from graduate school to postdoc to faculty level.

The other thing that's really changed is, when I was applying for jobs, I had people say, “Well, why should we hire you, when we could hire a man? You might have babies.” You could never say that now. Now all of the young people who want to have children have them. In fact, in one of our job searches a couple years ago, there was a young woman who came for an interview and had just had twins, something like six weeks before. My department chair asked me if I could help find a room for her to pump. It was no big deal.

I think in biology things are very good right now. I think other disciplines—physics, engineering—are not quite as good but they’re also coming up.

How do you manage work/life integration? Do you have tips for young scientists about this?

I always knew I wanted to have children. If I’d had to make a choice between having kids and having a career, I probably would have chosen to have children. It was great when I had my first child—I could go into lab when I felt like it and make my husband stay home with the baby. I didn't feel any pressure to not spend time with my kids.

I actually think having children helped me run a lab. I tend to treat the people who work for me as if they're my family. You don't yell at your family, you don’t yell at your children, and you don’t yell at your postdocs. Just be patient and loving.

If you weren’t a scientist, what other job would you have? Why?

Surprisingly, I'm a very good teacher. I say that’s surprising because I was so intimidated by the thought of teaching at first. I like to teach. I think it's a much harder job than doing research. I teach one undergraduate course in biology a year to Caltech students, and the class is usually very well regarded. Probably in a different era I would have been a high school teacher.

But, in reality, I can't imagine liking doing anything more than what I do.

This page last updated: August 9, 2018

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